Alzheimer's disease (AD) is a degenerative disorder characterized by a profound loss of memory and cognition. As patients exhibit a variety of symptoms, the disease has been found to be genetically heterogeneous also. Mutations in genes on chromosomes 21 (the -amyloid peptide) and 14 (presenilin 1) are associated with early onset disease, mutations in a gene on chromosome 1 (presenilin 2) with a Volga German kindred, and the risk factor apolipoprotein E n4 (Apon4) on chromosome 19 with both late-and-early onset disease. In this study, association of AD with both the ApoE n4 and ApoCI A alleles was found. The increased risk of AD among carriers of n4 was found to be higher among those who also bear the ApoCI A allele, but this may be due to a dose effect of the n4 allele.